The present inventions relate generally to an environmental barrier coating system for protecting components exposed to severe environmental and thermal conditions such as the hostile environment present in gas turbine engines. While the present inventions were developed for application in gas turbine engines utilization in other devices is contemplated herein.
Designers of gas turbine engines recognize that a limitation to the efficiency and emissions of many gas turbine engines is the temperature capability of metallic components (example, but not limited to blades, vanes, combustor liners) in the engine hot section. Although thermal barrier coatings are used to protect metallic components, thereby allowing the use of higher gas temperatures the metallic components remain a weak link.
Silicon-based ceramics, such as SiC/SiC composites and Si3N4 ceramics, are prime candidates for hot section components of gas turbine engines. One benefit of silicon-based ceramic engine components is their excellent high temperature mechanical, physical and chemical properties which allow gas turbine engines to operate at higher temperatures than current engines utilizing superalloy components. Higher engine operation temperature translates into significantly reduced emission (pollution) and increased fuel efficiency.
However, silicon based ceramic materials suffer from rapid recession in combustion environments due to the volatilization of silica scale by water vapor. This is a significant drawback in the utilization of silicon-based ceramics in gas turbine engines. Therefore, there is a need to identify techniques to limit/prevent the volatilization of silicon-based ceramics in engine operating environments. One technique is to utilize environmental barrier coatings (EBC) that provide the environmental protection for silicon-based ceramics. Current EBCs comprise a bond coat that provides the adherence onto the substrate and a topcoat that provides the environmental protection. The present inventions provide a novel and unobvious environmental barrier coating system.